1. Field
This invention relates to the use of UV light for the purification of air and water. It is particularly directed to apparatus and methodology specifically useful in clinical surroundings, notably dental operatories.
2. State of the Art
Ultraviolet (UV) radiation has been widely investigated for its potential utility in air and water purification applications. The portion of the electromagnetic spectrum having wave lengths between about 1000 and about 4000 .ANG. (angstrom units) is conventionally referred to as "ultraviolet light," even though it is not visible to the human eye. An angstrom unit is one ten billionth of a meter. The UV spectrum is alternatively defined as comprising wavelengths between about 100 and about 400 nm (nanometers). The UV portion of the spectrum is further arbitrarily divided into three band widths; specifically: UV-A (long-wave, above 320 nm), UV-B (medium wave, between about 280 and about 320 nm) and UV-C (short-wave, between about 100 and about 280 nm). UV-C radiation has been found to possess the greatest germicidal effectiveness, a wave length of 253.7 nm being commonly referred to as "germicidal UV."
UV-C radiation has been used commercially for air purification. U.S. Pat. No. 4,422,824, for example, discloses a ceiling fan with blades housing germicidal (UV) light bulbs. The blades are structured with chambers to direct air past the lights, thereby exposing airborne micro-organisms to UV light.
The germicidal effectiveness of UV-C radiation against both air-borne and water-borne microorganisms is discussed in the article "Ultraviolet Water Purification," Pollution Engineering Magazine, Vol. 5, No. 12, December, 1973. This article, the disclosure of which is incorporated by reference as a portion of this specification, describes practical constructions of germicidal lamps and water purification systems utilizing such lamps. Modem UV water treatment systems are disclosed by U.S. Pat. Nos. 5,401,394 and 5,536,395. The article, "Applications for Ultraviolet," Ann M. Wysocki, Water Conditioning and Purification Magazine, May 1988, describes a water purifier and proposes a number of practical applications for such a device. This article, which is incorporated by reference as a part of this specification, also details a set of criteria for an acceptable ultraviolet disinfecting unit.
One important consideration in the utilization of UV radiation in a space normally occupied by humans, is the safe exposure limit to such radiation. The National Institute for Occupational Safety and Health (NIOSH) has adopted as "safe" an exposure below the level found to cause eye irritation. In the case of germicidal UV (253.7 nm), the safe exposure limit is less than 0.2 .mu.watt/cm.sup.2 over any eight-hour period.
UV light has apparently not found practical application in dental operatories for air and water purification. U.S. Pat. No. 5,204,004 discloses a water line filtration system for dental operatories. The system is designed to prevent water flowing through a supply line to a hand piece from carrying bacterial contamination into a patient's mouth. The biofilm which normally forms in such a supply line is identified as a source of bacterial contamination for dental patients. U.S. Pat. No. 5,556,279 discloses a water purification system for dental instruments. The system is typical of equipment found in dental operatories, and consists of a disposable cartridge element comprising activated carbon and exchange resins disposed in a water supply line.